The Daily Grind: What attitudes can you not stand?

Blizzard has always been known by the fans for going all-out with their jokes on April 1st, and this year was no exception. The entire Equipment Potency Equivalence Number was funny in its own right, but especially as an attitude prevalent not only among World of Warcraft players. No matter what game you play, you know people whose sense of ego and importance at in-game achievements drives you up the wall. For some people it's a minor irritation; for others, it's the sort of thing that is so insufferable it's not worth even trying to work with them.

There are no shortage of helpful and friendly players in games, but there's also an abundance of arrogant gear worshippers, socially inept trolls, die-hard PvP grognards, ineffectual PvE carebears... you get the idea. Almost everyone agrees the extreme cases are bad, but we all think some are worse than others. So what about you? What sort of outlook makes you just quit a group in frustration no matter how the player performs? Is it something hugely removed from your own playstyle and approach, or something that's close to how you normally run and becomes more obnoxious as a result?